The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an inflatable bladder with internal tethers integrally formed as tear tabs on a bladder wall that limit the expansion of the bladder.
An active bolster is a type of vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deploying air bag cushions through various openings, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. Pending U.S. application Ser. No. 12/824,150, filed Jun. 26, 2010, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive.
In a typical structure, an active bolster includes a front wall or panel that faces a vehicle occupant and that is attached to a base wall (i.e., a reaction plate) along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. The walls are initially spaced apart while in their non-inflated condition to allow ingress of the inflation gas in a manner that achieves even inflation across the panel.
The front and base walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They can be blow molded or injection molded. Pending application Ser. No. 12/824,150 discloses frangible tabs formed in the base wall having surfaces that are joined with the front wall. The tabs act as hinges that control the expansion of the bladder. In particular, the tabs restrict expansion beyond the length of the tabs (i.e., they act as a tether that results in a desired bolster surface location for cushioning an impact). Prior to deployment and tearing of the tether tabs, the attachment between the tabs and the front wall also help reduce the oil canning effect. Oil canning is the springing in and out of a flat panel perpendicular to the plane of the panel. In addition to a drum-like noise, oil canning is undesirable because it gives a perception of lack of structural quality and integrity. Furthermore, vibrations during operation of a vehicle may become concentrated at the bolster, thereby creating additional noise. Other non-hinged interconnections may also be included between the base and front walls that completely separate during deployment as described in pending U.S. application Ser. No. 13/075,294, filed Mar. 30, 2011, incorporated herein by reference. The non-hinged interconnections may be just for the purpose of reducing oil canning and are easily separated during inflation of the bladder by the expansion gas.
By integrally forming the tether tabs as portions of one of the walls, the tethering function is obtained at a low manufacturing cost. Due to the hinged movement of the tether tabs, however, expansion of the bladder is imparted with a rotational component. In a typical placement of an active bolster, it is preferable to expand the bladder perpendicular to the interior trim surface and toward the occupant. Thus, the rotational component may be undesirable. It would be desirable to reduce the rotational component of the expansion (i.e., provide translational movement instead of rotation) while maintaining the low manufacturing cost of tether tabs integrally formed by a portion of the bladder walls.